2-Acetylbenzo[.beta.]thiophene and its substituted derivatives are useful intermediates in the production of valuable chemical end-products which include lubricant additives, rubber vulcanization accelerators, herbicides, dystuffs and pharmaceutical agents. For example, U.S. Pat. No. 4,873,259 discloses the use of substituted 2-acetylbenzo[.beta.]thiophenes as intermediates in the production of a class of N-hydroxyurea and acetohydroxamic acid compounds which have pharmacological activity as lipoxygenase inhibitors.
2-Acetylbenzo[.beta.]thiophene itself is a known compound, its synthesis in low yield reported by F. Mayer, et al., Ann., 488: 259-296 (1931) by the reaction between the sodium salt of 2-sulfhydrylbenzaldehyde and chloroacetone. A similar method of preparing 2-acylbenzo[.beta.]thiophenes by condensation of chloromethyl ketones with 2-sulfhydrylbenzaldehyde has been reported by M. Martynoff, et al., Bull. Soc. Chim., Section 5: 736-738 (1952). The preparation of 3-chloro-2-acetylbenzo[.beta.]thiophene by chlorination of 2-acetylbenzo[.beta.]thiophene is disclosed in U.S. Pat. No. 2,673,856. U.S. Pat. Nos. 2,634,200; 2,634,201; and 2,634,202 disclose herbicidal compositions containing 2-acylbenzo[.beta.]thiophenes prepared by the Lewis acid catalyzed reaction between benzo[.beta.]thiophene and acyl chlorides. M. W. Farrar, et al., J. Am. Chem. Soc.,: 4433-4436 (1950) report the preparation of 2-acetylbenzo[.beta.]thiophene by the acetylation of benzo[.beta.]thiophene with acetic anhydride in the presence of a Lewis acid catalyst.
The methods for preparing 2-acetylbenzo[.beta.]thiophene and its substituted derivatives which have been disclosed in the literature suffer from one or more of several shortcomings when evaluated as a commercially viable method of preparing 2-acetylbenzo[.beta.]thiophene. In some cases prior art processes involve acylation of benzo[.beta.]thiophene, a comparatively expensive starting material; in other cases, the starting material is 2-sulfhydrylbenzaldehyde, a comparatively unstable intermediate, difficult to synthesize. For example, D. Leaver, et al., J. Chem. Soc., 1962, 740, report the synthesis of reports the synthesis of 2-mercaptobenzaldehyde in 38% overall yield from 2,2'-dithiobis(benzoic acid) and M. F. Corrigan, et al., Aust. J. Chem., 29: 1413, (1976) report its synthesis in 14-17% overall yield from 2-nitrobenzaldehyde. H. Kasmai, et al., Synthesis, October 1989, pp. 763-765, report the synthesis of 2-mercaptobenzaldehyde in 52% overall yield from 2-mercaptobenzoic acid.
There is thus a need for a process for the preparation of 2-acetylbenzo[.beta.]thiophene and its derivatives which makes use of inexpensive, readily available, and chemically stable starting materials and intermediates and which produces the desired end-product in high overall yield and purity.